Carbon-13 Fourier Transform Nuclear Magnetic Resonance. IX. Complete Assignments of Some Prodigiosins. Bioincorporation of Label

Abstract

A comprehensive study has been made of the carbon-13 chemical shifts of substituted pyrroles. The data, together with perdeuteration, single resonance, and off-resonance techniques, formed the basis for the complete interpretation of the carbon-13 spectra of the prodigiosins. Based on these assignments the biosynthetic origin of the prodigiosin carbons was elucidated, with further biosynthetic studies to be reported.Carbon-13 chemical shifts are shown to be an effective means of determining sites of protonation.

13C Fourier Transform Nuclear Magnetic Resonance. XI. Pyridine N-Oxide Derivatives

“…We have previously reported on ring to sidechain long range couplings in pyrroles (18) and the present single resonance work provides further evidence for such interactions. Increased electron density at the C2,C6 and C, carbons due to the oxygen function cause a paramagnetic shift.…”

Conformational Preferences of 2-Acylpyrroles in Light of FT-IR and DFT Studies

“…It means that the population of the more polar anti-form increases with the increase in solvent polarity [75]. This effect was also observed for long chain N-substituted alkyl 2-acylpyrroles [71]. It would be expected on the basis of carbonyl absorption data that the N-H group could also show two absorption bands of the syn and anti-form spaced apart.…”

“…IR spectra revealed two carbonyl bands at 1658 and 1683 cm -1 for (35,36) and two ν C=O bands at 1662 and 1683 cm -1 for (33,34) whereas only one carbonyl band at 1681 cm -1 was found for N-methylpyrrol-2-yl trichloromethyl ketone (38) [41,42]. These IR data were surprising because according to earlier investigations we could expect to find only one ν CO band originating from the syn-form of N-methyl-2-acylpyrroles [70][71][72][73]. For instance, the IR spectrum of N-methylpyrrole-2-carboxylic acid, run in a non-polar solvent, shows single absorption of the carbonyl group [40].…”

“…There are also other N-alkyl-2-acylpyrroles such as N-methyl-, N-ethyl-, N-propyl, N-butylpyrroles which exist in solution in only one, the most stable syn-form. It is worth noting that long chain N-substituted alkyl 2-acylpyrroles easily adopt the synconformation [71].…”

“…There are also other N-alkyl-2-acylpyrroles such as N-methyl-, N-ethyl-, N-propyl, N-butylpyrroles which exist in solution in only one, the most stable syn-form. It is worth noting that long chain N-substituted alkyl 2-acylpyrroles easily adopt the synconformation [71].Infrared spectra of N-methyl 2-acylchloropyrroles (33-38) were also investigated in acetonitrile solution to distinguish the anti and the syn-rotamers [74]. It is noted that a method is available to discern the anti and the syn-rotamer.…”